At 7:53 PM -0800 2/4/02, Linus Toy wrote:
>sometime, I'll go get a pic and post, but in looking at the amp on
>one of my rears, the caps look fine...the transistors, though, look
>like something escaped. there's corrosion all over the heat-sink
>tab of the transistor and on the shield above. the PCB below looks
>heat-scorched.
Hmm...interesting. The shield on mine was also rusted up quite a
bit, but I didn't notice anything on the transistors immediately. I
assumed the rust was just because things are pretty wet etc in the
engine compartment, until I noticed something that was -really-
wierd...right near that speaker, on the bottom surface of the top of
the trunk(ie, if you were in the trunk lying upside down looking up)
was some corrosion or salts...a sort of "fuzz" that looked like
something had attacked the metal. Yikes.
Another thing I noticed was that there was an odd coating all over
the PCB from the bad unit that wasn't on either front speaker PCB.
It came off semi-easily with the CaiKleen44, so I suspected it was
some sort of coating applied by bose to make the unit more durable
for the trunk environment. I noticed that some of it ended up where
it shouldn't have, namely, between the ground shield/heat sink and
the transistors.
That -really- gets me thinking...I wonder if the stuff is insulating
the transistors from the heatsink, and causing them to overheat,
either short term or long term? If it is simply short term
overheating, it is easy enough to test, I can simply clean both
sides, slap it all back together quickly and see what it does just
plugged in sitting in the trunk. The other possibility is that it
was long-term damage from the thing overheating a lot.
Incidentally, both rear speaker failures have been on the driver's
side of the car(the reman unit I bought ended up on the passenger
side, passenger side unit ended up on the driver's side and has now
failed.)
I'm going to take a closer look at the transistors in a few minutes...
Brett
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